A Crystalline Unsupported Phosphagallene and Phosphaindene

The synthesis and isolation of TerP═GaTer and TerP═InTer (Ter = 2,6-Dipp₂-C₆H₃; Dipp = 2,6-diisopropylphenyl) is reported. These compounds feature unsupported P═Ga and P═In double bonds and two-coordinate triel element centers. Key to the stabilization of such compounds is the steric bulk of the terphenyl substituents, which serve to shield the highly reactive P═E bonds (E = Ga, In) and prevent further aggregation. When smaller aromatic substituents are employed on the phosphorus-containing precursor, the cyclic compounds Mes*P(ETer)₂ (Mes* = 2,4,6-^<i>t</i>Bu₃-C₆H₂) are isolated instead. These species contain weakly aromatic three-membered rings. The presence of an external base (PMe₃) is required in order to stabilize a phosphagallene when the smaller Mes* substituent is used, allowing for the isolation of Mes*P═GaTer(PMe₃).